You’ve been there. You attach a PDF to an email, hit send, and Gmail says “Attachment size exceeds the allowable limit.” Your file is 32MB and Gmail maxes out at 25MB. Now what?
Gmail suggests Google Drive. Outlook suggests OneDrive. But your recipient doesn’t want a link — they want the actual file. Their company firewall might block Drive links. Their email client might not preview Drive attachments. Or they just printed the last PDF you sent and want to do the same with this one.
The real fix is to make the PDF smaller. Not by removing pages. Not by lowering the resolution until it’s unreadable. Just by optimizing the file so it fits under the limit while still looking good.
Why PDFs get so big
A text-only PDF is tiny. A 50-page contract with no images might be 200KB. So why is your PDF 32MB?
Usually it’s one of these:
Embedded images at full resolution. A PDF with a few photos can easily hit 30-50MB because the images are stored at their original resolution — 4000×3000 pixels when they only display at 800×600 on the page. The PDF carries all those extra pixels.
Scanned documents. Each scanned page is a full-page image at 300-600 DPI. A 20-page scanned document at 300 DPI is easily 15-30MB. At 600 DPI it could be 60MB+.
Embedded fonts. PDFs embed fonts to ensure the document looks the same everywhere. If your document uses multiple fonts with full character sets, the font data adds up. Usually a few MB at most, but it contributes.
High-quality exports from design software. Documents exported from InDesign, Illustrator, or Photoshop are often saved at print quality — 300 DPI, CMYK color, no compression. Great for printing, way too big for email.
Email attachment limits
Different email services have different limits:
Gmail: 25MB per email (total, including all attachments combined)
Outlook/Office 365: 20MB default, configurable up to 150MB by admins
Yahoo Mail: 25MB
iCloud Mail: 20MB (larger files use Mail Drop)
ProtonMail: 25MB
The safe target is under 20MB — that clears every major email service.
How to compress a PDF (free options)
ConvertKr — upload the PDF, choose a quality level (Low for maximum compression, Medium for balanced, High for minimal quality loss), download the smaller version. Shows before/after file sizes so you can see exactly how much you saved. No account, processes in your browser.
iLovePDF Compress — good compression with three quality levels. Free with a few files per hour. Uploads to their servers.
SmallPDF Compress — one-click compression. Limited to 2 free tasks per day. $12/month after that.
Adobe Acrobat Online — has a compress feature. Requires Adobe account. Quality is good.
Preview (Mac) — open PDF in Preview, File > Export, select “Quartz Filter: Reduce File Size.” The compression is aggressive and sometimes makes text blurry, but it’s built in and works offline.
For a one-time compression, any of these works. If you compress regularly (weekly reports, client documents), a tool without daily limits is more practical.
What quality level should you choose?
This depends on what’s in the PDF and who’s receiving it.
Text-heavy documents (contracts, reports, letters): Use Medium or High compression. Text stays sharp at any compression level because text is stored as vectors, not images. The compression mostly affects embedded images. You can compress aggressively without visible quality loss on text.
Documents with photos (brochures, presentations, portfolios): Use Medium compression. Low might make photos noticeably blurry. Medium reduces size by 50-70% while keeping photos clear enough for screen viewing.
Scanned documents: Use Medium. Scanned pages are images, so compression directly affects readability. Medium gives a good balance — readable text, reasonable file size. Don’t go Low unless the text is large.
Print-quality documents you’re only emailing: Use High compression first. If the file is still too big, try Medium. Print-quality PDFs are often 10x larger than they need to be for screen viewing.
How much smaller will it get?
Realistic expectations:
A 30MB PDF with photos → 5-10MB at Medium quality
A 15MB scanned document → 3-5MB at Medium quality
A 50MB design export → 8-15MB at Medium quality
A 5MB text document → 2-3MB (text documents don’t compress as dramatically)
If your file is still too large after compression, you have two options: compress more aggressively (lower quality), or split the PDF into parts and send them as separate emails.
What if compression isn’t enough?
If your PDF is 100MB and you need it under 25MB, compression alone might not get you there without destroying quality. Alternative approaches:
Split into parts. Use a PDF splitter to break it into 2-3 parts. Email each part separately. “Attached is Part 1 of 3” is perfectly normal in business communication.
Remove unnecessary pages. Does the recipient actually need all 50 pages? If pages 30-50 are appendices they won’t read, remove them. Send the core document and offer to send appendices if needed.
Link to cloud storage. If the recipient is okay with links, upload to Google Drive, Dropbox, or OneDrive and share a link. Not always acceptable (some companies block external links) but often the easiest solution for very large files.
Compress and reduce resolution together. The compression tool reduces JPEG quality. If images in the PDF are at 600 DPI, they’ll be compressed but still large. For documents you’re only viewing on screen, 150 DPI is plenty. Some advanced tools let you specify the target DPI.
Gmail’s behavior with large attachments
When you try to attach a file over 25MB in Gmail, it automatically offers to upload it to Google Drive and insert a link instead. This works but has trade-offs:
The recipient gets a Drive link, not an attachment. They need to click the link, which opens in Drive, then download from there. Two extra steps.
If your Drive storage is full, the upload fails.
If you later delete the file from Drive, the recipient loses access.
Some corporate email systems strip Drive links or block external links entirely.
Compressing the PDF to fit under 25MB avoids all of these issues. The file arrives as a normal attachment that the recipient can open, save, and print directly.
Outlook’s attachment limit
Outlook’s default limit is more restrictive — 20MB for Office 365 personal accounts. Corporate Outlook accounts vary based on the admin’s settings, anywhere from 10MB to 150MB.
If you’re sending to someone at a large company, assume 10-20MB to be safe. Corporate email servers often have stricter limits than personal accounts.
Compressing for online forms and portals
It’s not just email. Many online submission portals have file size limits:
Job application portals: usually 2-5MB per file
Government form submissions: often 5-10MB
University application systems: 2-10MB per document
Insurance claim portals: varies, often 10-25MB
Court e-filing systems: varies by jurisdiction, some as low as 4MB per file
For these, you might need heavier compression. Medium or even Low quality to get a scanned document under 2MB. The quality trade-off is worth it — the recipient cares about readability, not print quality.
The privacy consideration
PDFs you email often contain sensitive information — financial reports, tax documents, legal agreements, medical records. Before uploading them to any compression tool, consider where the file goes.
ConvertKr compresses entirely in your browser — the file never leaves your device. Other tools upload to their servers and process in the cloud. For sensitive documents, browser-based processing is the safer option.
FAQ
Will the recipient notice the file was compressed?
For text documents, no — text stays sharp. For documents with photos, they might notice slightly reduced image quality if they zoom in, but at normal viewing size it looks the same.
Can I compress a password-protected PDF?
You’ll need to remove the password first, compress, then re-protect if needed.
Does compressing remove any content?
No. All pages, text, and images remain. Compression reduces the quality of embedded images and optimizes internal PDF structure, but nothing is removed.
Can I compress the same file multiple times?
Technically yes, but each round of compression further reduces image quality. Compress from the original each time with different settings, rather than compressing an already-compressed file.
Why is my compressed file larger than the original?
Rare, but it happens when the original is already highly optimized or contains mostly vector graphics and text. The compression process converts pages to images, which can actually increase size for files that were already small and vector-based.
What’s the smallest I can make a PDF?
A text-only PDF can be under 50KB. A document with images can realistically go down to about 100KB per page at low quality. Below that, text becomes unreadable.
PDF too big for email? Compress it here — choose your quality level, see the before/after sizes, download a smaller version. Or try splitting it into parts with the PDF splitter.